<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<div id="app">
    <p>{{date}}</p>
</div>
<script src="vue.global.js"></script>
<script>
    Vue.createApp({
        data() {
            return{
                date: '00:00:00'
            }
        },
        mounted(){
            setInterval(()=>{
                let d=new Date();
                this.date = d.getHours()+':'+d.getMinutes()+':'+d.getSeconds();
            },1000)
        }
    }).mount("#app")
</script>

</body>
</html>